Hard disk drives are common information storage devices essentially consisting of a series of rotatable disks that are accessed by magnetic reading and writing elements. These data transferring elements, commonly known as transducers, are typically carried by and embedded in a slider body that is held in a close relative position over discrete data tracks formed on a disk to permit a read or write operation to be carried out. In order to properly position the transducer with respect to the disk surface, an air bearing surface (ABS) formed on the slider body experiences a fluid air flow that provides sufficient lift force to “fly” the slider and transducer above the disk's data tracks. The high speed rotation of a magnetic disk generates a stream of air flow along its surface in a direction substantially parallel to the tangential velocity of the disk. The air flow cooperates with the ABS of the slider body which enables the slider to fly above the spinning disk. In effect, the suspended slider is physically separated from the disk surface through this self-actuating air bearing. The ABS of a slider is generally configured on the slider surface facing the rotating disk, and greatly influences its ability to fly over the disk under various conditions.
As portable devices such as handheld music/video players, cell phones, and digital cameras have become more prevalent, the market for small form factor (0.85″ to 1.8″) hard disk drives (SFF HDD) has increased substantially. SFF HDDs offer high recording capacity at a relatively inexpensive price. One design requirement critical for good reliability in SFF HDDs is a stable gap or flying height (FH) between the magnetic head (embedded in the slider) and the media (disk) in all possible environments where consumer electronics might be used.
The design of SFF HDDs presents many unique challenges. One such challenge is achieving a high enough flying height at very low linear speeds. The air bearing is generated by the air flow created by the rotation of the magnetic disk under the slider. A larger relative speed (i.e. a faster spinning disk or a disk with a larger radius) makes it easier to lift an air bearing. A typical speed at the inner diameter (“ID”) for a 3.5″ HDD like the ones used in desktop computers is approximately 18 m/s; while for a 0.85″ disk drive the speed at the ID is only approximately 2 m/s. This much lower speed makes it very difficult to generate enough air bearing force to fly the slider at a height that can avoid disk contact at the inner radius of a disk.
A related issue is the challenge of achieving a uniform flying height across the radii of the disk. The linear velocity of the disk increases at larger radii, making it more difficult to achieve a uniform flying height. In a typical 3.5″ HDD the sliders can be designed to reach a saturation level where the slider will continue to fly at a relatively constant height across varying radii (i.e. at varying linear velocities). Low linear velocities makes achieving a constant flying height across the radii of SFF HDDs more challenging.
Another challenge in designing SFF HDDs is large disk clamp distortion at the ID. SFF HDDs require thin disks, but thin disks usually have large distortions caused by disk clamping forces, leading to undulated disk surfaces and large FH variations at different radii. Disk distortion is typically more pronounced at the ID than at the OD.
In addition to the challenges mentioned above, there are many unique challenges presented by specific requirements of the consumer electronic devices that utilize SFF HDDs. For example, consumer electronics devices must operate in a large temperature range (from −20° C. to 80° C.). At varying temperatures, the slider and other disk drive components can experience thermal contraction or expansion. In order to achieve a stable flying height, an ABS design must compensate for the physical distortions that different temperatures can cause.
In addition to operating at a range of temperatures, consumer electronics and the SFF HDDs inside them must also be able to operate at different altitudes, ranging anywhere from below sea level to twenty thousand feet above sea level. The lower air density at high altitudes relative to sea level makes achieving an adequate lift force, and thus a stable flying height, more difficult.
Consumer electronics devices also have stringent shock requirements. The types of devices utilizing SFF HDDs frequently operate while moving and thus need to be able to withstand sudden impacts. A mechanical shock, such as being dropped to the ground, can cause the flying height between the magnetic head and the disk to suddenly change or even drop to zero, leading to head-disk contact. Therefore, an ABS design should be able to prevent head-disk contact under a certain level of shock.
In light of the foregoing challenges, a need in the art exists for an improved ABS design for use in SFF HDDs.